Spirit levels have heretofore been made with various different arrangements for mounting the level vial on the web portion of an I-shaped level frame and for orienting the level vial relative to the working surfaces of the frame. In some prior levels such as disclosed in U.S. Pat. Nos. 3,311,990; 3,738,015; 3,835,549; and 4,407,075, the level vials are mounted in diametrically opposed notches formed in the periphery of a vial opening in the frame, and vial case members are mounted on opposite sides of the web to retain the vials in the notches. The diametrically opposed notches must be precision formed to ensure that the vial is accurately positioned with respect to the working surfaces of the level body and, when it is desired to make a level in which level vials are mounted at several different angles with respect to the working surface, it is necessary to provide a plurality of pairs of such diametrically opposed notches. In some other prior levels such as disclosed in U.S. Pat. Nos. 2,810,206; 3,190,010; 3,593,428; 4,011,660 and 4,492,038, the level vials are mounted on or between a pair of opposed vial case members and the vial case members are attached to opposite sides of the web of the level frame by bolts or screws. Such arrangements usually require some angular adjustment of one or both case members in order to properly position the level vial with respect to the working surfaces of the frame, and this increases the cost of manufacture. In U.S. Pat. No. 4,124,940, one vial case member is provided with ears that extend into notches in the web of a level frame and the level vial is mounted on a second case member that is angularly adjustable relative to the first case member, to enable angular positioning of the vial with respect to the working surfaces of the level, and the case members are thereafter bonded together to hold the level vial in its adjusted position. In U.S. Pat. No. 4,581,828, the web is formed with a square opening and the level vial is mounted on one vial case having four pairs of tabs for engaging the opening in the web at the corners, and four camming posts are provided on the other vial holder to cam the tabs outwardly into engagement with the opening in the web, when the vial case members are drawn together against opposite sides of the web by screws that interconnect the case members.